AD 8375 output impedance

i found in datasheet that output impedance is 16K,but when i am trying  to simulate it in ADI SIM RF ver1.6,it shows input & output impedance is 150 Ohm only.which one is correct.

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    •  Analog Employees 
    on Dec 11, 2012 7:30 PM

    This is a structural issue with ADIsimRF.  Or to put it another way, the issue is how to fit the AD8375 into the ADIsimRF environment which expects each component to have real and relativelylow input and output impedances. The AD8375's output is a current source (hence the high output impedance). So its output voltage is formed by the output current and the load resistance. So with the output current driving a particular load resistance, we achieve all of the specs that are detailed in the datasheet (e.g. gain, IP3, Noise Figure, etc), even though the output stage does not look like the classically matched system that we expect in an RF signal chain. To fit the AD8375 and AD8376 into the ADIsimRF environment which recognizes and corrects for interstage mismatches,  we have to set the output impedance 150 ohms. If we set it to 16K ADIsimRF would apply a massive inter-stage mismatch RF Power loss.

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  • 0
    •  Analog Employees 
    on Dec 11, 2012 7:30 PM

    This is a structural issue with ADIsimRF.  Or to put it another way, the issue is how to fit the AD8375 into the ADIsimRF environment which expects each component to have real and relativelylow input and output impedances. The AD8375's output is a current source (hence the high output impedance). So its output voltage is formed by the output current and the load resistance. So with the output current driving a particular load resistance, we achieve all of the specs that are detailed in the datasheet (e.g. gain, IP3, Noise Figure, etc), even though the output stage does not look like the classically matched system that we expect in an RF signal chain. To fit the AD8375 and AD8376 into the ADIsimRF environment which recognizes and corrects for interstage mismatches,  we have to set the output impedance 150 ohms. If we set it to 16K ADIsimRF would apply a massive inter-stage mismatch RF Power loss.

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